The Federal Aviation Administration (FAA) requires all passenger carrying aircraft over 30 seats be equipped with so-called “Mode S” transponders. Mode S transponders are capable of transmitting a number (e.g., 25) of formats of coded data. This coded data includes such information as a unique 24-bit binary address for each aircraft.
The aircraft registration number may be derived from this 24-bit binary address. The coded Mode-S data also includes such information as aircraft altitude and may be transmitted continuously throughout a flight at a minimum rate of 1 Hz (i.e., once per second). Coded Mode-S data may be collected passively without any connection to air traffic control equipment.
The FAA has endorsed the Aircraft Communications Addressing and Reporting System (ACARS) system, which uses various data link technologies including the VHF communication band, HF and SATCOM along with a ground station network to allow aircraft to transmit and receive messages of coded data. Many domestic and international carriers have equipped their aircraft with ACARS equipment.
ACARS equipment is capable of transmitting a number of types of coded data. ACARS currently uses frequency shift keying (FSK) as a modulation scheme, however, other modulation schemes including minimum shift keying (MSK) and time division multiple access (TDMA) are being evaluated for future improvement of ACARS. ACARS data includes such information as the aircraft registration number and airline flight identification number (flight number).
ACARS transmissions from a single aircraft may be sent at varying intervals from as little as no transmissions in a single flight to several transmissions per minute. ACARS transmissions may be collected passively without any connection to air traffic control equipment.
None of the currently used or planned Mode S downlink formats provides for the transmission of flight identification data. There are a number of methods including Automatic Dependent Surveillance-Broadcast (ADS-B) and multilateration which allow for the precise determination of aircraft location through the Mode S downlink formats on a frequent basis. ACARS transmissions, while capable of encoding aircraft position and altitude, are not typically used for position determination as the frequency of ACARS transmissions may be too infrequent to allow one to accurately and timely determine the exact position of an aircraft.
Reducing noise from aircraft landing and taking off is a problem in the art. Determining which aircraft are violating noise restrictions is an essential part of the noise reduction problem. In the Prior Art, airports relied on post-processed flight track data (typically from airport radar systems) which would then be correlated with acoustical noise information and presented to management for analysis the next day or several days later. The acoustical data was usually collected by microphones or noise monitoring terminals located (NMTs) around the airport.
These NMTs would generally store a day's worth of noise information and then download that information each night for correlation with the post-processed flight tracks. However, since noise and flight track data may be not correlated until many hours after a noise event, it may be difficult if not impossible to respond to specific noise complaints or noise incidents, or to accurately determine post hoc which airplane caused which noise event. What is needed in the art is a system which allows for almost instantaneous correlation between noise data and flight tracks.
Triangulating on an aircraft's transponder signal may require decoding real-time transponder replies at several locations, time-stamping them and sending them to a central location for matching. Matching would attempt to pair up the transponder signals that had emanated from the same target.
An example of a Prior Art method for triangulating on an aircraft's transponder is disclosed in Wood, M., L., and Bush, R., W., Multilateration on Mode S and ATCRBS Signals at Atlanta's Hartsfield Airport, Lincoln Laboratory Project Report ATC-260, 8 Jan. 1998, incorporated herein by reference. In that method, triangulation on an aircraft's transponder relied on each remote sensor time-stamping all or most received transponder signals and passing them along to the central location for matching.
It was deemed necessary to do this since the remote sensor could not know which particular reply would be used by the central server for the matching process. This meant that a relatively high bandwidth communications medium was required between each remote sensor and the central server.
Such Prior Art methods used active interrogations to elicit the transponder replies, which allowed for some form of expectancy time for the replies. By scheduling interrogations the system estimated when replies might be received at each of the receivers and the system could then use windows in which to “listen” for replies. All replies received within these windows would then be time-stamped and then sent to the central server for matching.
This approach helped in some form to manage the required bandwidth on the link between the receiver and the central server. However, a relatively high bandwidth link is still required using this approach. Because of the practical bandwidth challenges in managing the link between the receivers and the central server it was generally thought in the Prior Art that using a completely passive approach for triangulation and multilateration would be impossible.
Multilateration and ASDI may be augmented with airline flight information available from an airlines flight reservation system. Dunsky et al, U.S. patent application Ser. No. 10/136,865, filed May 1, 2002 (Publication No. 2003/0009261 A1, published Jan. 9, 2003) entitled “Apparatus and method for providing live display of aircraft flight information”, incorporated herein by reference, describes the integration of Megadata's PAssive Secondary SUrveillance Radar (PASSUR) and airline flight information.